1. Field of the Invention
This invention relates generally to fiber optics and more particularly to fiber optic packaging.
2. Description of the Related Art
In circuit packaging, applications size and weight are a serious constraint. For example, the circuitry might have limited space available for the installation and a limited weight allowance. Moreover, environmental conditions that the circuit packaging is subjected to, such as mechanical vibration, can create additional packaging constraints for the structure. This can be true for electro-optic circuits as well as other types of associated circuits.
Structurally, a typical fiber optics cable includes a central clad core of silicate optical fiber. For protection the core is surrounded by additional concentric layers of a buffer coating of silicone, a first jacket for protection, a strength member of woven fibers such as graphite, for example, and an outer jacket for protection. A typical total diameter of this cable might be about 1,650 microns, with a weight of 3.0 kilograms/kilometer.
In packaging fiber optic cables with backplanes such as a printed circuit mother board, for example, one termini of the fiber optic cable includes a connector fitting that can be inserted through a clearance aperture in the backplane and coupled to an associated fiber optic element such as an optical module on the front surface or circuit mounting side of the backplane. The fiber optic cable extends over and parallel to the back surface or harness access side of the backplane. The other termini of the cable includes a connector fitting that might be coupled to a fiber optic buss.
The fiber optic cable typically requires a 90 degree bend in the direction of its axis to run it parallel to the surface of the backplane. If the radius of the bend is too small, the fiber optic core can be stressed and fracture or exhibit degraded optical transmission capabilities. Thus the fiber optic cables have typically been suspended from a frame that is secured to the back surface of the backplane. These frames can have a profile that extends several inches above the surface of the backplane. The individual cables are secured to the frame by loop type fasteners.
Another approach is to loop the end of the fiber optic cable above the backplane without support and then return it to the backplane and secure the individual cables to the backplane with some type of strap.
Both of these approaches require excessive amounts of space for high density packaging applications, and limit access to the backplane. Moreover, mechanical vibration can affect the package structure. For example, the relatively high profile frame has a relatively high center of gravity that creates a moment arm that, with the mass of the frame, can set up forces that can distort the frame and undesirably affect the fiber optics. The loops in turn are unsupported and can vibrate uncontrollably.
In addition, the other end of the fiber optic cable extends beyond the edge of the backplane and frame and as a result is unsupported. Thus it can be subject to strain, especially at the edge of the supporting structure.